Abstract: Tradeoffs are fundamental to lifehistory strategy theory, and the tradeoff between leaf size and leaf number is important for understanding the plant biomass allocation under different habitats. Based on the method of standardized major axis estimation (SMA), this paper studied the relationship between the leaf size and number of Robinia pseudoacacia plantations of different slope aspects in northern mountains of Lanzhou in semiarid region of Northwest China. The results indicated that with the change of the aspect from north to east, west and south, the cover and height of plant community and soil moisture declined, individual leaf area and individual lamina mass of R. pseudoacacia declined and the leafing intensity increased. Significant negative relationships between leafing intensity with individual leaf area and individual lamina mass were found in R. pseudoacacia in all aspects (P<0.05), and the common slope of the regressions was significantly close to -1. In addition, when the aspect changed from north to east, west and south, the four groups of yintercepts in the scaling relationships of leafing intensity with individual leaf area and individual lamina mass declined gradually. The tradeoff between leaf size and leaf number with changes in slope aspect of the habitat reflected the response and adaptation of plant functional traits to heterogeneous habitats and the balance mechanism of plant resource allocation.

Key words: photosynthesis, yield., maize, soil moisture, drip irrigation